Challenges from different courses seem to be "seeping" into each other

I've noticed that several challenges in the EN -> FR course went to the "Completed" tab, even though I'm positive I've never done them. I've done a lot more challenges in the DE -> EN course. And because at least some of the "misrouted" challenges from EN -> FR have a "sibling challenge" in DE -> EN, my guess is that they are somehow mistakenly synchronized.

For example, I recently did the English challenge about buying a bus ticket. The French challenge about buying a bus ticket went to the "Completed" tab, even though I haven't done that yet.

I added some annotations in red to highlight the relevant information. The problem occurs in the Android app, version 2.26.8 on my rather old Motorola G 2nd Generation with Android 6.0. I need to retire that device sooner rather than later, but so far it's chugging along pluckily

Hi @Henning-Kockerbeck, thanks for bringing it up. Would you please share a screenshot of the completed challenge about buying a bus ticket here or email it to bug@lingvist.io? I do not see it marked as completed in the EN>FR course.